Feature Request: Support multiple values for the same environment variable in custom schemes #3342

Motivation

Xcode's scheme editor allows several rows with the same environment variable name, each with its own checkbox. This is a convenient way to keep a menu of known values, for example OS_ACTIVITY_MODE rows for disable, info, and debug, or CFNETWORK_DIAGNOSTICS rows for 1, 2, and 3, with one of them checked.

Custom schemes cannot express this, because env in xcschemes.run, xcschemes.profile, and xcschemes.test is a dict, so each key carries exactly one value. Rows added by hand in Xcode are lost on the next regeneration.

Proposal

Allow an env value to also be a list of xcschemes.env_value entries. Each entry becomes one row for that key, in list order:

xcschemes.run(
    env = {
        "OS_ACTIVITY_MODE": [
            xcschemes.env_value("disable"),
            xcschemes.env_value("info", enabled = False),
            xcschemes.env_value("debug", enabled = False),
        ],
    },
)

This generates three OS_ACTIVITY_MODE rows with only disable enabled. Single values and "inherit" keep their current behavior.

Implementation

Only Starlark changes are needed: _env_infos_from_dict in xcscheme_infos.bzl would produce a list of values per key, and _add_env in xcschemes_execution.bzl would write the flattened count and one triple per entry. The generator already parses custom scheme variables into an array and writes them in order without deduplicating by key.

I am happy to open a pull request with the change, docs, tests, and a CHANGELOG entry.